1. Field of the Invention
The present invention relates to a surface mounting device-type light emitting diode (hereinafter, referred to as an SMD-type LED) which can enhance extraction efficiency of light to be emitted into the surface of a molding material which is exposed through an emission window of a package.
2. Description of the Related Art
Generally, a light emitting diode (hereinafter, referred to as ‘LED’) has a light source provided by varying compound semiconductor materials such as GaAs, AlGaAs, GaN, InGaInP and the like, thereby implementing various colors of light.
Recently, as the semiconductor technology rapidly develops, the production of LEDs with high luminance and high quality has become possible. Further, as the implementing of blue and white diodes with an excellent characteristic is realized, the use of LED is expanded into a display device, a next-generation lighting source, or the like. For example, SMD-type LEDs are productized.
Now, a conventional SMD-type LED will be described in detail with reference to FIGS. 1 to 4.
FIG. 1 is a schematic view illustrating the structure of a conventional SMD-type LED. The SMD-type LED 100 has a package 120 formed of molding epoxy resin or the like. The package 120 has an emission window formed on a predetermined surface thereof. The emission window is opened so that light is easily emitted through the emission window. On other surfaces of the package 120, a pair of lead terminals 130 is formed to project, the lead terminals 130 composing a lead frame to be mounted on a printed circuit board 110. Further, inside the package 120 constructed in such a manner, an LED chip (not shown) is disposed so that the light emission surface thereof is directed toward the emission window. The pair of lead terminals 130 and the LED chip are electrically connected through a wire (not shown).
FIG. 2 is a sectional view taken along II-II′ line of FIG. 1, showing the structure of the conventional SMD-type LED in detail.
As shown in FIG. 2, the conventional SMD-type LED 100 includes the pair of lead terminals 130, the package 120 formed to house a portion of the lead terminal 130 therein, the LED chip 140 mounted on a lead electrode inside the package 120, the wire 150 for electrically connecting the LED chip 140 and the lead electrode, and a molding material 160 filled in the package 120 so as to protect the LED chip 140 and the wire 150.
The molding material 160 for protecting the LED chip 140 is composed of transmissive resin including a transparent material or phosphor, depending on the color of an LED chip 140 to be implemented.
General standards for determining characteristics of LED chips include color, luminance, an intensity range of luminance and the like. Such characteristics are primarily determined by materials of compound semiconductors to be used in LED chips, but are incidentally influenced by the structure of a package for mounting an LED chip and a molding material filled in the package. Particularly, the molding material filled in the package has a large effect on the distribution of luminance.
In the conventional SMD-type LED, some of light is internally totally-reflected on the surface of the molding material, because of a large difference in refractive index between the molding material and the air, that is, at the interface with the vacuum, as shown in FIG. 3. In this case, the intensity of light to be emitted from the LED chip decreases, compared with that of light to be emitted from the LED chip without the molding material. Therefore, light efficiency decreases.
FIG. 3 is a conceptual diagram for explaining the reduction in luminance of an LED which is caused by the internal total reflection at the interface between the molding material and the vacuum.
Therefore, a new technique is being required, which minimizes internal total reflection of light caused by a molding material so as to increase the luminous intensity of an LED chip.
In the related art, a hemispheric lens 180 is attached to the surface of the molding material 160, which is exposed through the emission window of the package 120, by using a bonding layer 170, as shown in FIG. 4. Therefore, light to be emitted from the LED chip 140 is prevented from being internally totally-reflected on the surface of the molding material 160. Simultaneously, a light path is adjusted so that light extraction efficiency can be enhanced.
In the above-described SMD-type LED, however, the overall height thereof increases because of the lens 180. Therefore, the SMD-type LED cannot be used in a product having a limit in height. Further, water, ultraviolet (UV) or the like permeates through the bonding layer 170, thereby degrading reliability and characteristic.
Further, in order to attach the lens 180 to the surface of the molding material 160, additional separate processes are required, such as a lens manufacturing process, a position aligning process, a bonding process and the like. Such processes increase a manufacturing cost of an LED and increase a time required for the overall manufacturing process, thereby reducing a production yield of an SMD-type LED.